British visitors to France were warned yesterday about the risks of eating French beef, which government advisers believe poses a greater risk of "mad cow" disease than beef prepared in the UK.

British visitors to France were warned yesterday about the risks of eating French beef, which government advisers believe poses a greater risk of "mad cow" disease than beef prepared in the UK.

Professor Peter Smith, acting chairman of theGovernment's spongiform encephalopathy advisory committee (Seac), said eating beef in countries where mad cow disease was present could be more hazardous because health controls were slacker than in Britain.

He was specifically concerned with the fact that cows over 30 months of age are entering the human food chain in countries such as France and Portugal where there is a rising incidence of bovine spongiform encephalopathy (BSE).

A ban on cattle over 30 months is one of the principal safeguards in Britain against meat from cattle who are in the late stages of incubatingthe disease yet do not showany symptoms, Professor Smith said.

The Seac committee has told the Government it is "concerned" about the possible implications of subclinical infections - when animals are infected with BSE but show no symptoms - in countries where BSE is present but where there are less stringent controls than in Britain.

One member of Seac, Professor Harriet Kimbell, deputy chairwoman of the Consumers' Association, said she did not allow her children to eat beef when on holiday in France but did allow them to eat it in Britain.

"Tourists should be made aware that it may well be that British beef is now safer than it is in some other European countries," Professor Kimbell said.

"They [tourists] must make up their mind whether they want to incur the risk of eating beef elsewhere," she said.

Experiments have shown that the tissues of cattle under 30 months of age are far less infective than those from older cattle who are still healthy yet developing BSE.

Computer models predict that only one British cow incubating BSE will enter the food chain this year, whereas the number could be higher in countries such as France, even though they have a lower overall level of BSE. "There must be a number of cases being killed just before the develop BSE and show any signs of BSE. It is speculation but it is likely to be higher than one," Professor Smith said.

So far this year France has reported 66 cases of BSE compared with 960 in Britain. But the scale of the epidemic is declining in Britain and rising elsewhere.

Professor Smith said: "The protection we have in this country is largely because of the over 30-month rule. We think it's likely in some other countries that the number of animals going into the human food chain is likely to be larger than the UK because theydon't have the over 30-month rule in place. The ones that we are concerned about most are France and Portugal where there has been BSE. They certainly have far fewer cases but they are letting animals go into the food chain which would be far further into the incubation period," he said.

Last year, Britain imported about 10,000 tons of French beef, constituting some 10 per cent of the total imports from the European Union. Although the over 30-month rule still applies to imported beef, the Seac committee is concerned about its enforcement.

"There are controls in place to stop this happening, the question is how easy is it to do that because it is not possible to tell the age of beef on the slab," Professor Smith said. "We expressed our concern and this is obviously something that needs to be carefully looked at."